Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q41: TLS and Material LossFocus Recordings Available
|
Hide Abstracts |
Sponsoring Units: DQI DCMP DMP Chair: Kyle Serniak, MIT Lincoln Laboratory Room: McCormick Place W-196C |
Wednesday, March 16, 2022 3:00PM - 3:12PM |
Q41.00001: Engineering the phonon bath for TLS in a superconducting qubit Mo Chen, Oskar Painter Superconducting (SC) qubits are one of the leading platforms for fault-tolerant quantum computation. However, state-of-the-art SC qubits have a relatively short T1 lifetime and T2* coherence time compared to their atomic counterparts. One of the major limitations in the lifetimes of the SC qubits are the presence of various microscopic forms of two-level state (TLS) defects in the amorphous surface and/or bulk of the materials making up the qubits. Qubit decoherence is believed to come from a two step dissipation process in which: (i) the qubit state interacts first with the bath of TLS, and (ii) the TLS then interacts with the phonon bath of the bulk material. Previous work has focused mainly on mitigating the first step of the dissipation process by studying qubit-TLS interactions, and suppression of TLS effects via circuit design and new materials. |
Wednesday, March 16, 2022 3:12PM - 3:24PM |
Q41.00002: Study of Two-Level-System losses in Tantalum Superconducting Microwave Coplanar Waveguide Resonators AVEEK DUTTA, Alexander Place, Kevin D Crowley, Xuan Hoang Le, Youqi Gang, Xin Gui, Lila Rodgers, Trisha Madhavan, Nishaad P Khedkar, Ignace Jarrige, Yichen Jia, Mingzhao Liu, Adrian Hunt, Iradwikanari Waluyo, Steven Hulbert, Andi Barbour, Conan Weiland, Andrew L Walter, Robert J Cava, Andrew A Houck, Nathalie P de Leon
|
Wednesday, March 16, 2022 3:24PM - 3:36PM |
Q41.00003: Localization and mitigation of two-level system (TLS) and non-TLS losses at interfaces of niobium superconducting quantum resonators D. Frank Ogletree, Maria Virginia P Altoe, Archan Banerjee, Cassidy Berk, AHMED HAJR, Adam Schwartzberg, Chengyu Song, Michael Elowson, John Mark Kreikebaum, Ed K Wong, Sinead Griffin, Alexander Weber-Bargioni, Andrew M Minor, David I Santiago, Stefano Cabrini, Irfan Siddiqi We have characterized the metal-air (MA), substrate-air (SA) and metal-substrate (MS) interfaces of niobium-on-silicon resonators with cross-sectional scanning transmission electron microscopy (STEM) and x-ray photoemission spectroscopy (XPS). These resonators have a median internal loss tangent δint of 1.07 ppm at the single-photon level, with 71% due to two-level systems (TLS). We removed the SA process oxide by selective chemical etching, and reduced δint to 0.48 ppm, now 47% TLS. Next we reduced the MA oxide thickness from 4.8 to 1.6 nm in several steps, and further reducing δint to 0.19 ppm. We found that both TLS and non-TLS losses were uniformly distributed throughout the niobium process oxide. 70% of TLS losses were associated with the SA silicon oxide, 24% with the MA niobium oxide, and 6% other locations including the MS interface. In contrast only 17% of non-TLS losses came from SA, 68% from MA, and 15% from other locations. Together, the MA and SA interfaces accounted for at least 92% of loss. Interfacial materials analysis correlated with these observations gives some insight into host materials for TLS and non-TLS losses. Post-fabrication etching improved median internal quality factors from 0.93 million to 5.26 million. |
Wednesday, March 16, 2022 3:36PM - 4:12PM |
Q41.00004: Two-level system loss and noise, and development of superconducting integrated quantum processors Invited Speaker: Jonas Bylander We will show recent quantum hardware developments at Chalmers – materials, fabrication, design, and quantum algorithm implementations. |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q41.00005: Characterizing Loss Channels in Tantalum Transmons using Lumped Element Resonators Kevin D Crowley, Alexander P Place, AVEEK DUTTA, Sara F Sussman, Hoang Le, Youqi Gang, Nishaad P Khedkar, Nathalie P de Leon, Andrew A Houck Superconducting qubits based on tantalum have achieved record lifetimes and coherence times for planar transmons. The microscopic mechanisms for loss in these devices are poorly understood. In this talk, we present some progress in characterizing loss channels using lumped element (LE) resonators. Consisting of a capacitor and a meander inductor, LE resonators can be made to be geometrically representative of various kinds of transmon qubits, and can therefore be used to probe the loss channels that currently limit their coherence. By varying surface treatment, device geometry, device packaging, temperature, and power, we can separately characterize the effects of two-level systems (TLS's), bulk losses, and packaging on resonator coherence. We find that when the participation of surface oxides is minimized, the coherence of the LE resonators is limited by a temperature- and power-independent loss channel. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q41.00006: Low-loss parallel-plate capacitor for superconducting quantum circuits Alexander Melville, Wayne Woods, Kyle Serniak, Evan Golden, David K Kim, Bethany M Niedzielski, Kaidong Peng, Kevin P O'Brien, Jonilyn L Yoder, Mollie E Schwartz, William D Oliver Many coherent superconducting devices utilize coplanar waveguide resonators and co-planar (lateral) capacitors to avoid significant electric field participation in lossy dielectric surfaces and interfaces. The trade-off is a much larger footprint per device. In this work, we present a relatively low-loss parallel-plate capacitor that has a specific capacitance (~12 fF/µm2) that is orders of magnitude higher than for coplanar capacitors. The capacitor features <2% cross-chip variability and a loss tangent of approximately 2E-5. We have demonstrated T1 times of 6-20 µs in flux qubits shunted with this parallel-plate capacitor for varying degrees of designed electric-field participation. |
Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q41.00007: Fabrication and surface treatment of electron-beam evaporated niobium for low-loss coplanar waveguide resonators Daria Kowsari, Kaiwen Zheng, Jonathan T Monroe, Nathan J Thobaben, Xinyi Du, Patrick M Harrington, Erik A Henriksen, David S Wisbey, Kater W Murch We characterize low-loss electron-beam evaporated niobium thin films deposited under ultra-high vacuum conditions. Slow deposition yields films with a high superconducting transition temperature (9.20±0.06 K) as well as a residual resistivity ratio of 4.8. We fabricate the films into coplanar waveguide resonators to extract the intrinsic loss due to the presence of two-level-system fluctuators using microwave measurements. For a coplanar waveguide resonator gap of 2 μm, the films exhibit filling-factor-adjusted two-level-system loss tangents as low as 1.5×10−7 with single-photon regime internal quality factors in excess of one million after removing native surface oxides of the niobium. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q41.00008: Reducing two-level-system microwave loss in niobium resonators with nitrogen plasma passivation Kaiwen Zheng, Daria Kowsari, Nathan J Thobaben, Xinyi Du, Sheng Ran, Erik A Henriksen, David S Wisbey, Kater W Murch Microwave loss in niobium metallic structures used in superconducting quantum circuits is limited by a native oxide layer that grows back within hours after removal. This regrowth behavior prevents the incorporation of low loss niobium components in state-of-the-art superconducting quantum processors. We show that a low temperature nitrogen plasma treatment forms a 5 nm thick niobium nitride passivation layer which suppresses the presence of surface oxide. X-ray photoelectron spectroscopy measurements confirm the presence of nitrogen atoms and a suppressed oxygen concentration, which remain stable after 15 days of aging in an ambient environment. Cryogenic microwave transmission measurements of passivated niobium coplanar waveguide resonators reveal a filling factor adjusted two-level-system loss tangent that is 4 times lower than unpassivated devices. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q41.00009: TLS Fluctuations in Superconducting Circuits - Part 1 Jérémy H Béjanin, Matteo Mariantoni, Carolyn T Earnest, Alaa S Sharafeldin Amorphous dielectric materials have been known to host two-level systems (TLSs) for more than four decades. Recent developments on superconducting resonators and qubits enable detailed studies on the physics of TLSs. In particular, measuring the loss of a device over long time periods (a few days) allows us to investigate stochastic fluctuations due to the interaction between TLSs. We measure the energy relaxation time of a frequency-tunable planar superconducting qubit over time and frequency. The experiments show a variety of stochastic patterns that we are able to explain by means of extensive simulations. The model used in our simulations assumes a qubit interacting with high-frequency TLSs, which, in turn, interact with thermally activated low-frequency TLSs. Our simulations match the experiments and suggest the density of low-frequency TLSs is about three orders of magnitude larger than that of high-frequency ones. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q41.00010: TLS Fluctuations in Superconducting Circuits - Part 2 Yosri Ayadi, Jérémy H Béjanin, Christopher Xu, Cheng Zhu, Hamid R Mohebbi, Matteo Mariantoni At the single-photon regime and millikelvin temperatures, two-level systems (TLS) present in amorphous dielectric materials remain the main source of loss and noise in superconducting quantum devices. Superconducting microwave resonators, due to their low relaxation and decoherence rates and high sensitivity to noise, have long been used to investigate the physics of TLSs. In addition, their ease of fabrication and simpler measurement requirements make them a convenient experimental platform. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q41.00011: Titanium Nitride Film on Sapphire Substrate with Low Dielectric Loss for Superconducting Qubit Hao Deng, Tian Xia, Ran Gao, Zhijun Song Coherence times of superconducting qubits are often limited by dielectric loss of the materials. Among multiple candidates of material systems, the combination of titanium nitride (TiN) film and sapphire substrate shows its potential because of the crystallinity, chemical stability against oxidization, and high quality at interfaces. In this work, we report TiN films deposited by magneto sputtering on sapphire substrate achieving low dielectric loss on the substrate-metal (SM) interface. We systematically characterize a series of 2D transmons fabricated with identical batches of TiN base layer, but with different geometries of qubit shunting capacitors covering various participation ratios of SM interface. We then quantitatively extract a loss tangent at the SM interface smaller than 7.5 × 10−4 in 1 nm disordered layer. With such low level of dielectric loss, the optimal relaxation time (T1) and decoherence time (T2, spin echo) of 2D transmon reach up to 302.2 us and 165.4 us respectively. This work suggests that TiN films on sapphire substrate are an ideal material system for long-coherence superconducting qubits. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q41.00012: Detection of TLS defects coupled to a c-shunt flux qubit via critical-current fluctuations Leonid Abdurakhimov, Imran Mahboob, Hiraku Toida, Kosuke Kakuyanagi, Yuichiro Matsuzaki, Shiro Saito Two-level-system (TLS) defects in superconducting qubits are one of the major noise mechanisms limiting qubit coherences. TLS defects are various atomic-scale defects of different microscopic nature which are mainly formed in amorphous layers such as the aluminum-oxide tunnel barrier of an Al/AlOx/Al Josephson junction. Conventionally, it is assumed that charge TLS defects are coupled to a superconducting qubit via charge fluctuations. However, TLS defects can also interact with a qubit through critical-current fluctuations, although such type of interaction has not been detected in experiments consistently. |
Wednesday, March 16, 2022 5:48PM - 6:00PM |
Q41.00013: Compact vacuum gap transmons - selective and sensitive probes for superconductor surface losses Martin Zemlicka, Elena Redchenko, Matilda Peruzzo, Farid Hassani Bijarbooneh, Andrea Trioni, Shabir Barzanjeh, Johannes Fink The large capacitor of state-of-the-art transmon qubits systematically lowers the coupling to parasitic losses localized in material interfaces, but it also lowers the achievable integration density of quantum processors, and increases unwanted radiation losses, cross-couplings and leakage. We fabricate and characterize transmons with a footprint area as low as 36 x 39 μm2 and show that the interaction with the lossy dielectric interfaces is rapidly decreased by using very narrow (≥ 100 nm) capacitor vacuum gaps. We utilize commercial silicon-on-insulator wafers, where the sidewalls of suspended silicon beams are metalized by angle evaporation such that up to 99.6% of the electric field energy is distributed in vacuum and the effective dielectric constant is close to unity. Measuring the internal quality factor of lumped element resonators and the energy relaxation time of qubits hence allows to precisely probe the superconductor surface loss properties and isolate a single loss channel – two level defects in the aluminum surface oxide exposed to ambient conditions. This offers new means to systematically improve coherence times by testing appropriate superconducting materials and surface treatments. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700